The electric drive assembly of a machine typically provides a primary power source, such as an internal combustion engine, or the like, a generator, a power circuit and one or more traction motors coupled to one or more drive wheels or traction devices. When the machine is propelled, mechanical power produced by the primary power source, or engine, is converted to electrical power at the generator. This electrical power is often processed and/or conditioned by the power circuit before being supplied to the traction motors. Moreover, the power circuit selectively activates the traction motors at a desired torque so as to cause movement of the drive wheels. The traction motors transform the electrical power back into mechanical power in order to drive the wheels and propel the electric drive machine or vehicle.
The machine is retarded in a mode of operation during which the operator desires to decelerate the electric drive machine. To retard the machine in this mode, power from the primary power source or engine is reduced. Typical machines also include brakes and other types of retarding mechanisms to decelerate and/or stop the machine. As the machine decelerates, the momentum of the machine is transferred to the traction motors via rotation of the drive wheels. The traction motors act as generators to convert the kinetic energy of the machine into electrical power that is supplied to the electric drive assembly. This electrical energy can be dissipated through storage, waste, or any other form of consumption by the electric drive assembly in order to absorb the machine's kinetic energy. Currently existing electric drive machines or vehicles commonly employ at least a retarding grid assembly through which large amounts of kinetic energy is dissipated in the form of heat.
A typical electrical retarding grid assembly includes a series of resistive elements and insulators through which thermal energy is dissipated while electrical current passes therethrough. Due to the size of machine components and the magnitude of the momentum being retarded, large amounts of thermal energy may be dissipated through the resistive elements and insulators. Such magnitudes of thermal energy can significantly elevate the temperatures of the resistive elements and insulators of the associated retarding grids, and if it is not appropriately managed, can be detrimental to the overall operation of the associated electric drive machine.
Various solutions in the past have employed active cooling systems, such as forced convection by use of a fan or blower, to create airflow over the resistive elements and insulators of retarding grids and reduce the temperatures thereof. While such active cooling systems can compensate for temperature changes in the resistive elements of retarding grids, such systems cannot fully account for temperature changes in the insulators of retarding grids. More specifically, the insulators of a retarding grid are susceptible to hotspots or uneven distribution of temperatures, as well as overshoot conditions or sudden increases in temperature upon blower shut off. The temperatures of insulators which result from such hotspots and overshoot conditions can greatly exceed allowed thresholds and still be undetected by currently existing cooling solutions.
Accordingly, there is a need to provide a more robust and reliable means for minimizing overheating conditions of retarding grids associated with electric drive machines without relying solely on passive and/or active cooling solutions. Moreover, there is a need to preemptively limit the energy that is passed onto the resistive elements and insulators of retarding grids. The disclosed systems and methods are directed at addressing one or more of the needs set forth above.